Ventilation hoods are critical to protecting workers from airborne contaminant exposures, yet the experimental and theoretical knowledge about simple benchtop enclosing hoods provides an insufficient underpining for design practice. This objective of this study is to provide a strong basis for design decisions regarding the most important variables encountered in the field. In addition, the study will answer fundamental questions concerning how key variables affect the protection efficiency. The specific aims are to determine the effects of hood airflow, cross-draft velocity, orientation, and hood size. Additional variables include spatial variability of hood face velocities, aerodynamic entries, and use of a flip up sash. Numerical simulation (CFD) using a 3-D laser scan of the manikin will: 1) allow extrapolation and interpolation to other conditions, 2) help explain the underlying mechanisms responsible for contaminant transport, 3) help develop simple mathematical models of the effects of variables on hood performance. Particle image velocimetry will allow visualization and quantification of flow fields, providing the potential to find transitions visually. Experiments will be performed in a 9' high, 12' wide, 50 ft long wind tunnel using ethanol as a tracer gas (<100ppm) to expose both human subjects and an anthropomorphic, heated, breathing manikin. The human subjects will do makework tasks while working at each hood. The manikin will be posed as if doing the same work. Each test condition will be replicated, with tests and replicatication mixed in a single random order. Air velocities will be determined using a particle image velocimeter (PIV) and a 2-D constant temperature anenometer. Results from the experimental findings will be used to cross-validate CFD predictions. Human and manikin results will be compared to allow validation of manikins as surrogates for humans and to provide a basis of comparison to studies done using only manikins. [unreadable] [unreadable] [unreadable]